A more thorough explanation:

A subpoena is a written order that requires a person to give testimony on a specific subject. This can happen in court or other legal proceedings, like a Congressional inquiry. If someone ignores a subpoena, they can be punished for contempt.

For example, if a person witnessed a crime and the prosecutor wants them to testify in court, they can issue a subpoena to make sure the witness shows up. Another example is if a company is being investigated for fraud, the government can issue a subpoena to get access to the company's financial records.

Subpoenas are an important tool in the legal system to make sure people provide evidence and testimony when needed.